The present invention relates to an in-plane switching liquid crystal display apparatus obtained by adhering two substrates, at least one of which comprise electrodes of comb-like shape, together and enclosing liquid crystal therebetween. More particularly, the present invention relates to a liquid crystal display apparatus which can restrict variations in display property such as color changes or the like depending on visual angles.
Liquid crystal display apparatuses are being widely used in watches or electronic desk calculators due to their properties of being, for instance, thin-sized, light-weighted and of consuming low electricity. Especially TN (twisted nematic) liquid crystal display apparatuses which perform active driving through, for instance, TFTs (thin film transistors) are gradually replacing CRTs which are display apparatuses of word processors or personal computers. However, such a TN liquid crystal display apparatus presents a drawback in view of display quality in that reversals of tones are generated with respect to certain visual angles arid contrast values thus change. For the aim of improving the reliability of display quality on visual angles, it has been tried in Japanese Unexamined Patent Publication 76125/1996 to expand the visual angle by dividing display pixels into multiple regions. However, the region of visual angles in which reversals of tunes did not occur was only as large as xc2x140xc2x0 to lateral directions and xe2x88x9220xc2x0 to +10xc2x0 in vertical directions, and thus insufficient for actual use.
There are recently being suggested in-plane switching liquid crystal display apparatuses which completely differ from TN type liquid crystal display apparatuses in their driving methods, examples of which are disclosed in xe2x80x9cNikkei Micro Devicesxe2x80x9d by Nikkei BP, December 1995 edition, P.130 to 135, or in xe2x80x9cCollection of Preliminary Drafts of the Semicom Kansai 96 FPD Technical Seminarxe2x80x9d by SEMI Japan, May 30, 1996, P. 3 to 23, 3 to 27 and P. 4 to 19, 4 to 21. Since liquid crystal molecules are to be switched to an electric field in a plane parallel with respect to the substrate, there are fewer variations in display property depending on visual angles than compared to TN liquid crystal display apparatuses and thus are of favorable display property.
FIG. 13 is a partial explanatory view of a conventional in-plane switching liquid crystal display apparatus which is formed by using liquid crystal which are of positive dielectric anisotropy. In FIG. 13, there are shown, from among components of the liquid crystal display apparatus, an electrodes substrate, two types of comb-like shaped electrodes (hereinafter referred to as xe2x80x9ccomb-like electrodesxe2x80x9d) formed on the electrodes substrate, and liquid crystal molecules (only four of those are shown in the drawings) which are included in the counter substrate and a liquid crystal layer, which together constitute a liquid crystal panel. As shown in FIG. 13, the electrodes substrate 2 with the comb-like electrodes 1 is disposed parallel to counter substrate 3, and between the electrodes substrate 2 and the counter substrate 3, there exists a liquid crystal layer including liquid crystal molecules 4 which are oriented substantially in parallel directions with respect to a longitudinal direction of the comb-like portions of the comb-like electrodes 1.
Next, the display theory of the liquid crystal display apparatus will be explained based on FIG. 14. FIG. 14 is a partial explanatory view showing the in-plane switching liquid crystal display apparatus. In FIG. 14, there are only shown a liquid crystal panel and two polarizers from among components of the liquid crystal display apparatus, and of the liquid crystal panel, there are only shown an electrodes substrate, respective comb-teeth portions of two types of comb-like electrodes (one each of each comb-teeth portion), a counter substrate, and liquid crystal molecules (only seven of these are shown in the drawings) included in the liquid crystal layer. In FIG. 14, numeral la denotes a first comb-like electrode, 1b a second comb-like electrode, numeral 2 an electrodes substrate, numeral 3 a counter substrate, numeral 4 liquid crystal molecules in the liquid crystal layer, numeral 5 a first polarizer, arid numeral 6 a second polarizer. As shown in the drawings, the first polarizer 5 is disposed such that a longitudinal direction of the liquid crystal molecules 4 (a direction indicated by xe2x80x9cNxe2x80x9d in the drawings) is parallel to a transmission axis O of the first polarizer 5, and the second polarizer 6 is disposed such that a transmission axis P of the second polarizer 6 is orthogonal with respect to the transmission axis O of the first polarizer 5. It should be noted that the aligning direction (a direction indicated by xe2x80x9cQxe2x80x9d in the drawings) of alignment layers (not shown) formed on surfaces of the electrodes substrate 2 and the counter, substrate 3 are parallel with respect to transmission axes O, P of the first polarizer 5 and the second polarizer. The thickness of the liquid crystal layer is defined as d. Further, the transmission axes are parallel with respect to an oscillating direction of light that has passed through the polarizer.
In case the electric field is OFF (that is, no electric field is generated between the first comb-like electrode 1a and the second comb-like electrode 1b), the oscillating direction of an incident linear polarized light, that has passed through the first polarizer 5, is parallel to the aligning direction of the liquid crystal molecules, and since it is not affected by birefringence at the time of passing through the liquid crystal layer, the oscillating direction R1 of light passing through the counter substrate 3 is made orthogonal to the transmission axis P of the second polarizer 6, and light that has passed through the counter substrate 3 being impossible of passing through the polarizer 6, a dark condition is obtained. It should be noted that since no outgoing transmission light exists in dark conditions, arrow I1 is indicated as a broken line in the drawings.
In case the electric field is ON (that is, an electric field 1c is generated between the first comb-like electrode la and the second comb-like electrode 1b), the liquid crystal molecules 4 rotate in a direction of the electric field (note that the degree of rotation depends on the size of the electric field) while maintaining a parallel orientation (or alignment) with respect to the electrodes substrate 2 and the counter substrate 3. Therefore, the incident linear polarized light is affected by birefringence, changes into an elliptical polarization R2, and a predetermined amount of light passes through the second polarizer 6. It should be noted that the amount of light passing through the second polarizer 6 is dependent on inclinations of liquid crystal molecules in a longitudinal direction (a direction indicated by xe2x80x9cTxe2x80x9d in the drawings). Here, the rotating angle xcex8 is expressed by applied voltage (V). In this manner, display is performed by performing ON/OFF operations of applied voltage to the first comb-like electrode and the second comb-like electrode.
The strength of transmission light I is given by equation (1).
I=I0 sin2(xcfx80R/xcex)sin22xcex8(V)xe2x80x83xe2x80x83(1)
where I0 represents the strength of incident light to the first polarizer 5, xcex a wavelength of incident light, and R retardation which is expressed by optical-path difference of ordinary light and extraordinary light (xcex94n) xc2x7d, where xcex94n is an absolute value (|no-ne|) of a difference between a refractive index of ordinary light no and refractive index of extraordinary light ne of liquid crystal.
As it is evident from equation (1), intensity of the transmission light becomes maximum when xcex8=xcfx80/4. Further, intensity of the transmission light outgoing from the second polarizer 6 is expressed by a function of a wavelength of incident light xcex and retardation R.
FIG. 15 is a graph showing dependence of transmittance on wavelength of various retardation values R (R=200 nm, 275 nm, 300 nm) in case of xcex8=xcfx80/4. In FIG. 15, the vertical axis represents the transmittance (%) and the lateral axis represents the wavelength xcex (nm). With transmittance, it is meant a ratio of the amount of light that has passed through the second polarizer to the amount of light that is incident on the first polarizer. In FIG. 15, the dependency of transmittance on wavelength in case the retardation value R is 200 nm is shown by a solid line, the dependence of transmittance on wavelength in case the retardation value R is 275 nm is shown by a broken line, and the dependence of transmittance on wavelength in case the retardation value R is 300 nm is shown by a two-dot chain line. It is evident from FIG. 15 that the dependence of transmittance on wavelength is largely effected by retardation values.
FIG. 16 is an explanatory view showing an alignment condition of liquid crystal molecules of a conventional in-plane switching liquid crystal display apparatus. In the in-plane switching liquid crystal display apparatus, each of the liquid crystal molecules 4 are aligned in a direction denoted by numeral 22 with respect to the electrodes substrate 2 and counter substrate 3, respectively, at pretilt angles 13 each directed into different directions. This alignment condition is defined as parallel alignment. Pretilt angle 13 indicates an inclination of the liquid crystal molecules 4 in a longitudinal direction 4a with respect to the surface of the electrodes substrate 2 (or the counter substrate 3).
In this case, the refractive index anisotropy of the liquid crystal layer differs in case the liquid crystal panel is looked at from the direction with respect to the surface of the counter substrate 3 and in case when the liquid crystal panel is looked at from direction b, since the liquid crystal molecules 4 are aligned at parallel alignment at their pretilt angles 13, whereby the retardation value R that is obtained by multiplying birefringence rate xcex94n by cell gap d (that is, xcex94nxc2x7d) is varied. This, in turn, resulted in variations in dependence of transmittance on wavelength, and caused degradations in display quality since the display was colored blue (wavelength 440 nm) when looked at from a certain angle, and yellow (wavelength 580 nm) when looked at from another direction. Further, it was also presented a drawback in that the display property depending on visual angles became asymmetric with respect to the front of the liquid crystal panel, so that the display quality was degraded. In other words, while property dependent on visual angles were improved in conventional in-plane switching liquid crystal display apparatuses than compared to TN liquid crystal display apparatuses, there still remains problems that depending on visual angles, coloring occurred or display property varied.
The present invention has been made with the aim of restricting coloring and degradations in display quality depending on visual angles, and it is an object thereof to provide an in-plane switching liquid crystal display apparatus in which degradations of display quality such as coloring which are dependent on visual angles hardly occur.
The liquid crystal display apparatus according to claim 1 of the present invention is a liquid crystal display apparatus comprising:
(1) a liquid crystal panel including an electrodes substrate provided with pixel electrodes and counter electrodes, a counter substrate which opposes the electrodes substrate, and a liquid crystal layer containing therein liquid crystal molecules which are driven by an electric field that is generated in a substantially parallel manner with respect to a surface of the electrodes substrate when voltage is applied on the pixel electrodes and counter electrodes; and
(2) a driving circuit for supplying predetermined electric signals to the pixel electrodes and the counter electrodes,
wherein inclining directions of liquid crystal molecules which are closest to the electrodes substrate and those of liquid crystal molecules which are closest to the counter substrate are identical, and aligning directions of liquid crystal molecules which are closest to the electrodes substrate and those of liquid crystal molecules which are closest to the counter substrate are parallel to each other.
In the liquid crystal display apparatus according to claim 2 of the present invention, the pixel electrodes and counter electrodes are comb-like electrodes.
In the liquid crystal display apparatus according to claim 3 of the present invention, the pixel electrodes and counter electrodes are comb-like electrodes, and longitudinal directions of comb-teeth portions of the comb-like electrodes are aligned to be parallel to each other.
The liquid crystal display apparatus according to claim 4 of the present invention is a liquid crystal display apparatus comprising:
(1) a liquid crystal panel including an electrodes substrate provided with pixel electrodes and counter electrodes, a counter substrate which opposes the electrodes substrate, and a liquid crystal layer containing therein liquid crystal molecules which are driven by an electric field that is generated in a substantially parallel manner with respect to a surface of the electrodes substrate when voltage is applied on the pixel electrodes and counter electrodes; and
(2) a driving circuit for supplying predetermined electric signals to the pixel electrodes and the counter electrodes, wherein a display region of the liquid crystal panel includes a plurality of pixels that are arranged in a form of a matrix, and each of the pixels are divided into a plurality of regions in which aligning directions of liquid crystal molecules are different from each other.
In the liquid crystal display apparatus according to claim 5 of the present invention, the pixel electrodes and counter electrodes are comb-like electrodes.
In the liquid crystal display apparatus according to claim 6 of the present invention, the pixel electrodes and counter electrodes are comb-like electrodes, and longitudinal directions of comb-teeth portions of the comb-like electrodes are aligned to be parallel to each other.
The liquid crystal display apparatus according to claim 7 of the present invention is a liquid crystal display apparatus comprising:
(1) a liquid crystal panel including an electrodes substrate provided with pixel electrodes and counter electrodes, a counter substrate which opposes the electrodes substrate, and a liquid crystal layer containing therein liquid crystal molecules which are driven by an electric field that is generated in a substantially parallel manner with respect to a surface of the electrodes substrate when voltage is applied on the pixel electrodes and counter electrodes; and
(2) a driving circuit for supplying specified electric signals to the pixel electrodes and the counter electrodes, wherein an optical compensation layer is provided on a surface of the liquid crystal panel facing to persons looking thereat.
In the liquid crystal display apparatus according to claim 8 of the present invention, the pixel electrodes and counter electrodes are comb-like electrodes.
In the liquid crystal display apparatus according to claim 9 of the present invention, the pixel electrodes and counter electrodes are comb-like electrodes, and longitudinal directions of comb-teeth portions of the comb-like electrodes are aligned to be parallel to each other.